Optical fiber heat dissipation package

ABSTRACT

A heat-dissipation package for use with an optical fiber includes a base, a cover, and a hollow sleeve. The base includes an upper surface, a lower surface, and a groove embedded in the upper surface, the groove having a generally U-shaped cross-sectional shape. The cover is positioned on the upper surface of the base. The sleeve includes a cylindrical inner surface and an outer surface with a first portion which has a generally U-shaped cross section and a second portion which has a generally planar cross section such that edges of the planar cross section contact an open end of the U-shaped cross section. The first portion of the outer surface of the sleeve is positioned in the groove and the second portion of the outer surface of the sleeve is in contact with the cover. The sleeve is configured to encapsulate a heat-generating section of the optical fiber.

RELATED APPLICATION

The current patent application is a continuation patent applicationwhich claims priority benefit with regard to all common subject matterto U.S. patent application Ser. No. 15/584,612, titled “OPTICAL FIBERHEAT DISSIPATION PACKAGE”, and filed May 2, 2017. The earlier-filedutility application is hereby incorporated by reference in its entiretyinto the current patent application.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the current invention relate to packaging for use withoptical fibers.

Description of the Related Art

Optical fiber laser systems 100, such as the exemplary system of priorart FIG. 1, may include a lasing pump source 102, a high reflectoroptical fiber 104, a gain optical fiber 106, and an output coupleroptical fiber 108. The lasing pump source 102 may be provided by aplurality of laser diodes 110 and a pump combiner 112. Each laser diode110 may generate laser light. The pump combiner 112 may opticallycombine the laser light from the laser diodes 110. The high reflectoroptical fiber 104 may include a fiber Bragg grating (FBG) which acts asa mirror. The gain optical fiber 106 may be spliced to the highreflector optical fiber 104 and may be doped with elements such asytterbium or erbium to act as a gain medium. The output coupler opticalfiber 108 may be spliced to the gain optical fiber 106 and may includean FBG which acts as a partial mirror. The light output from the pumpcombiner 112 may be coupled into the high reflector optical fiber 104,which along with the gain optical fiber 106 and the output coupleroptical fiber 108 form an optical resonator. The laser beam may beprovided by the output coupler optical fiber 108 or a delivery opticalfiber spliced thereto.

The FBG of the high reflector optical fiber 104 and the output coupleroptical fiber 108 typically absorbs a small fraction of the incominglight. Contaminants that remain at the glass surface of the opticalfiber after the fabrication of an FBG can also absorb some of the lightpropagating inside the fiber. This absorption by the FBG and surfacecontaminants may produce heat and an ensuing temperature increase thatcan be sizable when the incoming optical power reaches kilowatt levels.The FBG and surrounding materials may not be able to withstand thistemperature increase without sacrificing performance metrics such asspectral response.

SUMMARY OF THE INVENTION

Embodiments of the current invention solve the above-mentioned problemsand provide a distinct advance in the art of optical fiber packaging.Specifically, embodiments of the current invention provide aheat-dissipation package that effectively removes heat from the claddingof an optical fiber implemented with a fiber Bragg grating. Theheat-dissipation package may broadly comprise a base, a cover, and ahollow sleeve. The base includes an upper surface, a lower surface, anda groove embedded in the upper surface, the groove having a generallyU-shaped cross-sectional shape. The cover is positioned on the uppersurface of the base. The sleeve includes a cylindrical inner surface andan outer surface with a first portion which has a generally U-shapedcross section and a second portion which has a generally planar crosssection such that edges of the planar cross section contact an open endof the U-shaped cross section. The first portion of the outer surface ofthe sleeve is positioned in the groove and the second portion of theouter surface of the sleeve is in contact with the cover. The sleeve isconfigured to encapsulate a heat-generating section of the opticalfiber.

Another embodiment of the current invention may provide aheat-dissipation package for use with an optical fiber that broadlycomprises a housing and a submount. The housing includes a centralcavity and opposing ends, each end having a channel configured toreceive a portion of the optical fiber. The submount is positioned inthe central cavity and includes a base, a cover, two fiber supportblocks, and a hollow sleeve. The base includes an upper surface, a lowersurface, two opposing end surfaces, and a groove embedded in the uppersurface. The groove has a generally U-shaped cross-sectional shape, witheach end surface including a pedestal extending longitudinallytherefrom. The cover includes an upper surface, a lower surface and twoopposing end surfaces, with each end surface including an overhangextending longitudinally therefrom. One fiber support block ispositioned in each of the spaces created between one overhang and onecorresponding pedestal. Each fiber support block includes a through holeand is configured to receive a portion of the optical fiber in thethrough hole. The sleeve includes a cylindrical inner surface and anouter surface with a first portion which has a generally U-shaped crosssection and a second portion which has a generally planar cross sectionsuch that edges of the planar cross section contact an open end of theU-shaped cross section. The first portion of the outer surface of thesleeve is positioned in the groove and the second portion of the outersurface of the sleeve is in contact with the cover. The sleeve isconfigured to encapsulate the heat-generating section of the opticalfiber.

Yet another embodiment of the current invention may provide an opticalfiber laser system component broadly comprising an optical fiber, abase, a cover, and a hollow sleeve. The optical fiber has a fiber Bragggrating section and includes a core which is surrounded by at least onecladding which is surrounded by at least one coating layer. The fiberBragg grating section includes the core surrounded by the cladding. Thebase includes an upper surface, a lower surface, and a groove embeddedin the upper surface, the groove having a generally U-shapedcross-sectional shape. The cover is positioned on the upper surface ofthe base. The sleeve includes a cylindrical inner surface and an outersurface with a first portion which has a generally U-shaped crosssection and a second portion which has a generally planar cross sectionsuch that edges of the planar cross section contact an open end of theU-shaped cross section. The first portion of the outer surface of thesleeve is positioned in the groove and the second portion of the outersurface of the sleeve is in contact with the cover. The sleeve isconfigured to encapsulate the fiber Bragg grating section of the opticalfiber.

Still another embodiment of the current invention may provide an opticalfiber assembly broadly comprising first and second optical fibers, abase, a cover, and a hollow sleeve. The optical fibers are splicedtogether with a fiber splice. Each optical fiber includes a core whichis surrounded by at least one cladding which is surrounded by at leastone coating layer and a stripped section which abuts the fiber splice.The stripped section includes the core surrounded by the at least onecladding. The base includes an upper surface, a lower surface, and agroove embedded in the upper surface, the groove having a generallyU-shaped cross-sectional shape. The cover is positioned on the uppersurface of the base. The sleeve includes a cylindrical inner surface andan outer surface with a first portion which has a generally U-shapedcross section and a second portion which has a generally planar crosssection such that edges of the planar cross section contact an open endof the U-shaped cross section. The first portion of the outer surface ofthe sleeve is positioned in the groove and the second portion of theouter surface of the sleeve is in contact with the cover. The sleeve isconfigured to encapsulate the stripped sections of the first and secondoptical fibers.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Other aspectsand advantages of the current invention will be apparent from thefollowing detailed description of the embodiments and the accompanyingdrawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the current invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a schematic block diagram of a prior art optical fiber lasersystem;

FIG. 2 is a perspective view of a heat-dissipation package, constructedin accordance with various embodiments of the current invention, for usewith an optical fiber;

FIG. 3 is an exploded view of the heat-dissipation package including ahousing and a submount;

FIG. 4 is an exploded view of the submount including a base, a cover,two support blocks, and a sleeve;

FIG. 5 is a cross-sectional view of one end of the heat-dissipationpackage, cut along line 5-5 of FIG. 2, depicting the interface of theoptical fiber and the package;

FIG. 6 is a cross-sectional view of the submount cut along a verticalplane transverse to the longitudinal axis depicting the base, the cover,the sleeve, and the optical fiber encapsulated by the sleeve;

FIG. 7 is a perspective view of an end of a first embodiment of theoptical fiber including a mechanical protection coating, a cladding, anda core;

FIG. 8 is a perspective view of an end of a second embodiment of theoptical fiber including a secondary coating, a primary low-indexcoating, a cladding, and a core;

FIG. 9 is cross-sectional view of the optical fiber, cut along an axialplane, depicting the core with a first embodiment of a fiber Bragggrating;

FIG. 10 is cross-sectional view of the optical fiber, cut along an axialplane, depicting the core with a second embodiment of a fiber Bragggrating;

FIG. 11 is a perspective view of an optical fiber assembly, constructedin accordance with additional embodiments of the current invention, theassembly including a fiber splice;

FIG. 12 is an exploded view of the optical fiber assembly of FIG. 11including a housing and a submount; and

FIG. 13 is an exploded view of the submount of the assembly depictingthe fiber splice.

The drawing figures do not limit the current invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description of the invention references theaccompanying drawings that illustrate specific embodiments in which theinvention can be practiced. The embodiments are intended to describeaspects of the invention in sufficient detail to enable those skilled inthe art to practice the invention. Other embodiments can be utilized andchanges can be made without departing from the scope of the presentinvention. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment”, “an embodiment”, or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc. described in one embodiment mayalso be included in other embodiments, but is not necessarily included.Thus, the current technology can include a variety of combinationsand/or integrations of the embodiments described herein.

A heat-dissipation package 10, constructed in accordance with variousembodiments of the current invention, for use with optical fibers 200 inan optical fiber laser system 100 is shown in FIGS. 2-6. A firstheat-dissipation package 10 may retain the high reflector optical fiber104 and a second heat dissipation package 10 may retain the outputcoupler optical fiber 108 in the optical fiber laser system 100 of FIG.1.

The optical fiber 200 may generally have an exemplary structure thatincludes a central core 202, a coaxial cladding 204, and a coaxialcoating 206, as seen in FIG. 7. The core 202 and the cladding 204 mayeach be formed from a glass material with the index of refraction of thecladding 204 being less than the index of refraction of the core 202.The coating 206 may be formed from a polymer material and generallyprovides mechanical protection and minimizes stress for the cladding204.

In another embodiment, the optical fiber 200 may include a central core202, a coaxial cladding 204, a coaxial first coating 208, and a coaxialsecond coating 210, as seen in FIG. 8. As above, the core 202 and thecladding 204 may each be formed from a glass material with the index ofrefraction of the cladding 204 being less than the index of refractionof the core 202. The first coating 208 may be from a polymer material,such as a soft, low-index fluoroacrylate polymer, that has an index ofrefraction less than the index of refraction of the cladding 204.Typically, the difference in index of refraction between the firstcoating 208 and the cladding 204 is much greater than the difference inindex of refraction between the cladding 204 and the core 202 in orderto minimize penetration of light from the cladding 204 to the firstcoating 208 and to be able to inject light into the cladding 204 insteadof just the core 202. The second coating 210 may be formed from apolymer material and generally provides mechanical protection. Such afiber is typically used in a high-power laser system 100 where thecladding 204 is used to guide the light output from the pump combiner112. As known in the art, a fiber of the type illustrated in FIG. 8 mayhave more than one cladding made of glass (not illustrated).

When the optical fiber 200 is utilized as the high reflector opticalfiber 104 or the output coupler optical fiber 108, the core 202 of theoptical fiber 200 may include a fiber Bragg grating (FBG) 212. Anexemplary FBG 212 may include a periodical modulation of the index ofrefraction 214 extending along the longitudinal axis of the opticalfiber. In a first embodiment, seen in FIG. 9, the modulation of theindex of refraction has a uniform period. In a second embodiment, seenin FIG. 10, the period of the modulation of the index of refractionvaries axially, which forms a chirped FBG 212. The FBG 212 within theoptical fiber 200 creates an optical reflector for laser light. Thewavelength of the light reflected by the FBG 212 may vary according to,at least, the period of the modulation of the index of refraction 214and the average value of the index of refraction. The strength of thereflection depends on a length of the grating and an amplitude of theindex modulation.

The heat-dissipation package 10 may broadly comprise a housing 12 and asubmount 14, as best seen in FIG. 3. The housing 12 may include a body16 and a lid 18. The body 16 may be of generally solid elongatedrectangular box shape with an upper surface, a lower surface, two sidesurfaces, and two end surfaces. The upper surface may be recessed fromthe tops of the side surfaces. The body 16 may include an elongatedcavity 20 with two end channels 22. The cavity 20 may be positioned inthe center of the body 16 and aligned with the longitudinal axisthereof. The end channels 22 are longitudinal axis aligned as well andextend from the cavity 20 to each end surface. The body 16 may alsoinclude a plurality of through holes from the top surface to the bottomsurface configured to receive screws, or the like, to mount the package10 to an external surface. In some embodiments, the body 16 may furtherinclude two flanges, each extending from one side surface adjacent tothe bottom surface.

The lid 18 may be of generally elongated rectangular shape andrelatively thin compared to its length and width. The lid 18 may includea top surface, a bottom surface, two side edges, and two end edges. Thelid 18 may also include through holes from the top surface to the bottomsurface which align with the through holes of the body 16. The body 16may be formed from material with high thermal conductivity andmechanical strength.

The submount 14 may comprise a base 24, a cover 26, first and secondfiber support blocks 28, and a sleeve 30, as best seen in FIG. 4. Thebase 24 may also be of generally solid elongated rectangular box shapewith an upper surface, a lower surface, two side surfaces, and two endsurfaces. The base 24 may further include first and second pedestals 32,each of which extends outward longitudinally from one of the endsurfaces adjacent to the lower surface, as seen in FIGS. 4 and 5. Insome embodiments, a corner of the joint between each pedestal 32 and itscorresponding end surface may be rounded. In addition, the base 24 mayinclude a groove 34 in the upper surface extending along a central axisline. The groove 34 may have a U-shaped cross section. In alternativeembodiments, the groove 34 may have other cross-sectional shapes, suchas semi-circular, semi-oval, semi-elliptical, triangular, square,rectangular, etc.

The cover 26 may be of generally solid elongated rectangular box shapewith an upper surface, a lower surface, two side surfaces, and two endsurfaces. In certain embodiments, the cover 26 may include a groovetypically with a complementary cross-sectional shape to that of thegroove 34 in the base 24. The cover 26 may further include first andsecond overhangs 36, each of which extends outward longitudinally fromone of the end surfaces adjacent to the upper surface, as seen in FIGS.4 and 5. In some embodiments, a corner of the joint between eachoverhang 36 and its corresponding end surface may be rounded. The base24 and the cover 26 may each be formed from material with a high thermalconductivity.

Each fiber support block 28 may be of generally solid elongatedrectangular box shape with an upper surface, a lower surface, two sidesurfaces, and two end surfaces, as seen in FIGS. 4 and 5. In someembodiments, the corners between one end surface and the upper and lowersurfaces may be rounded. Each fiber support block 28 may further includea through hole 38 extending, transverse from the longitudinal axis ofthe block 28, from one end surface to the opposing end surface. Inaddition, the through hole 38 may include a first section with a firstdiameter and a second section with a second diameter, wherein the firstdiameter is less than the second diameter. Each fiber support block 28may be formed from a polymer material with an index of refraction thatis less than the index of refraction of the cladding 204 of the opticalfiber 200.

The sleeve 30 may be hollow with a cylindrical inner surface that has acircular cross-sectional shape. The sleeve 30 may have an outer surfacewith a U-shaped cross section, such that a first portion of the outersurface forms a U shape and a second portion of the outer surface isplanar and couples with the open end of the first portion, as best seenin FIG. 6. The sleeve 30 may be utilized to encapsulate the cladding 204of the optical fiber 200 in region where the optical fiber 200 includesthe FBG 212. Therefore, the sleeve 30 may have a longitudinal axiallength that is approximately equal to the length of the FBG 212. In someembodiments, the ends of the sleeve 30 may extend beyond the ends of theFBG 212 by a predetermined length. The sleeve 30 may be formed from apolymer material with an index of refraction that is less than the indexof refraction of the cladding 204 of the optical fiber 200.

The submount 14 may have a construction as follows. The sleeve 30 may beconfigured to receive, retain, and/or encapsulate a portion of thelongitudinal axial length of the cladding 204 and the core 202 of anoptical fiber 200 such that an outer surface of the cladding 204 is inphysical contact with the inner surface of the sleeve 30. (Coatings onthe optical fiber 200 are removed before the optical fiber 200 isimplemented with the heat-dissipation package 10.) The sleeve 30 may bepositioned within the groove 34 of the base 24 such that the U-shapedportion of the outer surface of the sleeve 30 is in physical contactwith the groove 34. The cover 26 may be positioned on the base 24 suchthat the lower surface of the cover 26 is in physical contact with theupper surface of the base 24 and the planar portion of the outer surfaceof the sleeve 30. The cover 26 may be attached to the base 24 withadhesives, fasteners, or the like. Once the cover 26 is on the base 24,the ends of the sleeve 30 may align with the end surfaces of the cover26 and the base 24.

The assembly of the base 24 and the cover 26 may form two spaces, onespace at each end of the submount 14 between one overhang 36 and onecorresponding pedestal 32. As seen in FIGS. 3 and 5, one fiber supportblock 28 may be positioned within each space, such that the uppersurface of the fiber support block 28 physically contacts the overhang36, the lower surface of the fiber support block 28 physically contactsthe pedestal 32, and one end surface of the fiber support block 28physically contacts at least a portion of the end surfaces of the base24 and the cover 26. Furthermore, each end of the sleeve 30 mayphysically contact a portion of one end surface of one fiber supportblock 28. In addition, the through hole 38 of each fiber support block28 may be configured to receive and/or retain a portion of the opticalfiber 200 such that the cladding 204 and the core 202 of the opticalfiber 200 are positioned in the first section of the through hole 38,and the coating 206, the cladding 204, and the core 202 of the opticalfiber 200 are positioned in the second section of the through hole 38,as illustrated in FIG. 5. When the optical fiber has two coatings asillustrated in FIG. 8, the second section of the through hole 38 may beconfigured to receive the second coating 210, the first coating 208, thecladding 204 and the core 202 (not illustrated).

The heat-dissipation package 10 may have a construction as follows. Thesubmount 14 may be positioned in the cavity 20 such that the lowersurface of the base 24 contacts the body 16 of the housing 12. Inaddition, the optical fiber 200 is retained by the submount 14 andextends through the end channels 22. The optical fiber 200 may beattached to the housing 12 with an adhesive in each end channel 22, orwithin the cavity 20 adjacent to each end channel 22. In variousembodiments, the end channels 22 may be filled with a soft material (notshown in the figures) such as silicone to minimize the mechanical forcesacting on the optical fiber 200. The lid 18 may be positioned in therecess on the top surface of the body 16 and may be attached theretowith adhesives and/or fasteners.

At least one of the functions of the heat-dissipation package 10 istransfer or remove heat from the FBG 212 of the optical fiber 200 whenthe optical fiber 200 is used as the high reflector optical fiber 104 orthe output coupler optical fiber 108 in an optical fiber laser system100. In various implementations of the optical fiber laser system 100,light may be coupled into the core 202 and the cladding 204 of theoptical fiber 200 from the pump combiner 112. In such a case, thepackage must also maintain the transmission of light in the cladding204. Hence, the index of refraction of the hollow sleeve 30 must besmaller than the index of refraction of the fiber cladding 204. Anexemplary low-index material may include a fluoroacrylate polymer.Furthermore, the thickness of the sleeve 30 should be relatively largein order to ensure that light guided in the cladding 204 does not reachthe outer boundary of the sleeve 30. The hollow sleeve must also allow agood flow of heat in order to limit temperature increases at the fiber200. To this end, the thermal resistance of the hollow sleeve 30 betweenthe fiber cladding 204 and the base 24 may be less than approximately1.5×10⁻⁴ degree Kelvin meter² per Watt (° Km²/W). Typically, the sleeve30 is formed from material that has a low value of thermal conductivity.For example, the thermal conductivity of fluoroacrylate can be as smallas approximately 0.2 Watts per meter degree Kelvin (W/m° K). Thus, thethickness (from the inner surface to the outer surface) of the sleeve 30should be small to provide sufficient heat transfer away from theoptical fiber 200. For optimum performance, the sleeve 30 made of afluoroacrylate may have a thickness ranging from approximately 5 micronsto approximately 30 microns, along its smallest dimension such as therounded part of the U-shaped outer surface, perhaps best seen in FIG. 6.

The fiber support blocks 28 are also in direct contact with the opticalfiber 200, as seen in FIG. 5, and may be formed from a material with thesame properties as the sleeve 30. An exemplary material from which thefiber support blocks 28 are formed may include a fluoroacrylate polymer.

The base 24 and the cover 26 of the submount 14 may provide, among otherfeatures, transfer or removal of heat from the sleeve 30 and may beformed from materials with high thermal conductivity. However, thematerials should also have a CTE similar to that of the fiber 200, beeasy to manufacture, and have a reasonable cost, among other properties.Other considerations for the materials may include transmission of, ortransparency to, ultraviolet (UV) wavelength radiation. In someinstances, the sleeve 30 may be formed, or coated, on the cladding 204of the optical fiber 200 by using a separate, external mold or by usingother methods. In other instances, the sleeve 30 may be formed, orcoated, on the cladding 204 while the cladding 204 is positioned in thebase 24 with the cover 26 attached. In such circumstances, UV lighttransmitted through the cover 26 could be used to cure the material ofthe sleeve 30.

Exemplary materials that may be used to form the base 24 and the cover26 include synthetic diamond, copper, aluminum, silicon, tungsten,synthetic sapphire, multispectral zinc sulphide, or the like. Syntheticdiamond has an extremely high thermal conductivity and a CTE that isclose to that of the optical fiber 200. However, its low availabilityand high cost make it impractical for a commercial product. Copper andaluminum have high thermal conductivities and are easily machined, butthey also have a high CTE—making them incompatible with the opticalfiber 200. Silicon and tungsten have relatively high thermalconductivities and CTEs which are closer to that of the optical fiber200 than are copper and aluminum. Synthetic sapphire and multispectralzinc sulphide have CTEs which are closer to that of the optical fiber200 than are copper and aluminum, but their thermal conductivities arerelatively low. However, synthetic sapphire and multispectral zincsulphide have the advantage of being transmissive to UV light. Thus, ifthe sleeve 30 is separately formed, then the base 24 and the cover 26may each be formed from either silicon or tungsten. Alternatively, onemay be formed from silicon, while the other is formed from tungsten. Ifthe sleeve 30 is to be UV cured in the base 24 with the cover 26attached, then typically the cover 26 may be formed from eithersynthetic sapphire or multispectral zinc sulphide. When the cover 26 isformed from either synthetic sapphire or multispectral zinc sulphide,the base 24 may be formed from silicon or tungsten. An exemplarymaterial from which the base 24 is formed may have a thermalconductivity greater than 50 W/m° K and a CTE less than 5×10⁻⁶/° K. Anexemplary material from which the cover 26 is formed may have a thermalconductivity greater than 20 W/m° K and a CTE less than 7×10⁻⁶/° K.

The housing 12 may provide, among other features, transfer or removal ofheat from the submount 14. Generally, heat may transfer from thesubmount 14 to the housing 12 through the interface of the lower surfaceof the base 24 and the body 16 when the submount 14 is positioned withinthe cavity 20 of the housing 12. The body 16 may be formed frommaterials with high thermal conductivity. The body 16 may have similarconstraints to those of the base 24. For reasons similar to thosediscussed above, an exemplary material for forming the body 16 mayinclude tungsten. An exemplary material from which the body 16 is formedmay have a thermal conductivity greater than 50 W/m° K and a CTE lessthan 5×10⁻⁶/° K.

The heat-dissipation package 10, that is constructed with the sleeve 30having the dimensions discussed and with all of the components beingformed from the materials discussed, may have a thermal slope of 0.005degrees Celsius per Watt (° C./W), wherein the thermal slope of anobject is the amount of temperature increase of the object for theamount of power applied to it. The thermal slope applies to thetemperature increase per watt of pump power in the cladding 204 as wellas to the temperature increase per watt of signal power in the fibercore 202. The thermal slope of the heat-dissipation package 10 of thecurrent invention allows for multiple kilowatts of power to be appliedwhile maintaining a temperature of the components of the package 10 andthe optical fiber 200 that is within acceptable parameters.

It is generally desired to limit the temperature of the coatings of theoptical fiber 200 in order to maintain structural integrity of thecoating. For example, the temperature of a fluoroacrylate coating shouldbe kept at less than or equal to approximately 70° C. This temperatureconstraint also applies to the sleeve 30 of the heat-dissipation package10, since the sleeve 30 encapsulates the cladding 204 in the samefashion as the coatings. In an exemplary optical fiber laser system 100,a pump power of 5 kilowatts (kW) and a signal power of 5 kW may beapplied, resulting in a temperature increase of 50° C. (0.005° C./W×10kW). This leads to the sleeve 30 having a temperature of 70° C.,assuming that the temperature of the base 24 is 20° C. In contrast, ahigh reflector optical fiber 104 with two coating layers as illustratedin FIG. 8, that would normally be utilized in an optical fiber lasersystem 100 may have a thermal slope of 0.05° C./W. Therefore, the highreflector optical fiber 104, without the heat-dissipation package 10 ofthe current invention, would be able to handle only 10% of the appliedpower before the temperature of the coatings exceeds the safe operatingtemperature of 70° C. Furthermore, the heat-dissipation package 10 ofthe current invention may minimize hot spots created by contaminants atthe surface of the optical fiber 200 which generate temperaturegradients along the FBG 212 that will spoil its spectral response.

In addition, when the components of the submount 14 and the housing 12are formed from materials with the ranges of values of CTEs that arediscussed above, the optical fiber 200 that is retained in theheat-dissipation package 10 is better able to withstand the thermalstresses which occur when a large pump power and a large signal powerare applied. Also, since the optical fiber 200 is attached to thehousing 12 at two axially spaced apart points, there is a slight tensionon the fiber 200 that is less likely to vary when the materialsconstituting the package 10 have CTEs that are more closely matched tothat of the optical fiber 200. Therefore, the heat-dissipation package10 of the current invention may offer greater structural reliability andimproved spectral response.

The heat-dissipation package 10 may also be utilized with the packagingof two optical fibers 200A, 200B of the type illustrated in FIG. 8 thatare to be spliced to one another, which creates an optical fiberassembly 300, as shown in FIGS. 11-13. As an example, one end of eachoptical fiber 200A, 200B may be stripped of its coating layers leaving astripped section with just the cladding 204 and the core 202. The endsof the optical fibers 200A and 200B may be fused together, creating asingle optical fiber 200 which includes a fiber splice 302 and has alength that is just cladding 204 and core 202. Without using theheat-dissipation package 10, the cladding 204 and core 202 could berecoated with one or more layers, and the optical fiber 200 could beutilized in a normal fashion. However, the stripping and recoatingprocedure may leave contaminants at the surface of the optical fibers200A and 200B, which absorb optical power propagating in the cladding204 and generate heat. As a result, performance of the spliced opticalfiber 200 would suffer. To avoid this situation, the spliced cladding204 and core 202 may be encapsulated by the sleeve 30, and the rest ofthe optical fiber 200 may be positioned in the heat-dissipation package10 as described above. The heat-dissipation package 10 may remove theheat generated at the splice while preserving the transmission ofoptical power through the optical fiber 200.

In another embodiment of the current invention, the heat-dissipationpackage 10 may be combined with the optical fiber 200 including the FBG212 to create the high reflector optical fiber 104 or the output coupleroptical fiber 108. The high reflector optical fiber 104 or the outputcoupler optical fiber 108 may be constructed as shown in FIG. 2, whereinat least one end of the optical fiber 200 may be spliced to the gainoptical fiber 106 to form the optical resonator portion of the opticalfiber laser system 100.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

Having thus described various embodiments of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:
 1. A heat-dissipation package for use with an opticalfiber with a heat-generating section, the optical fiber including a corewhich is surrounded by at least one cladding which is surrounded by atleast one coating layer, the heat-generating section including the coreand the at least one cladding and occupying a portion of an axial lengthof the optical fiber, the heat-dissipation package comprising: a baseincluding an upper surface, a lower surface, two opposing end surfaces,and a groove embedded in the upper surface, the groove having agenerally U-shaped cross-sectional shape; a cover including an uppersurface, a lower surface, and two opposing end surfaces, the coverpositioned on the upper surface of the base; and a hollow sleeveincluding a cylindrical inner surface and an outer surface with a firstportion which has a generally U-shaped cross section and a secondportion which has a generally planar cross section such that edges ofthe planar cross section contact an open end of the U-shaped crosssection, the first portion of the outer surface of the sleeve positionedin the groove and the second portion of the outer surface of the sleevein contact with the cover, the sleeve configured to encapsulate theheat-generating section of the optical fiber.
 2. The heat-dissipationpackage of claim 1, further comprising two fiber support blocks, eachfiber support block of generally rectangular box shape and eachincluding a through hole with a first section having a first diameterand a second section having a second diameter, the first diameter beingless than the second diameter, each fiber support block configured toreceive a portion of the optical fiber in the through hole such that thefirst section receives the core and the at least one cladding and thesecond section receives the core, the at least one cladding, and the atleast one coating layer.
 3. The heat-dissipation package of claim 2,wherein the base further includes two pedestals, each pedestal extendingoutward longitudinally from one end surface adjacent to the lowersurface, the cover further includes two overhangs, each overhangextending outward longitudinally from one end surface adjacent to theupper surface, and each fiber support block is positioned in the spacebetween one pedestal and one corresponding overhang.
 4. Theheat-dissipation package of claim 2, wherein the fiber support blocksare formed of a material with an index of refraction smaller than theindex of refraction of the at least one cladding.
 5. Theheat-dissipation package of claim 2, wherein the fiber support blocksare formed from a fluoroacrylate polymer.
 6. The heat-dissipationpackage of claim 1, wherein the sleeve is formed from a material thathas a thermal resistance less than 1.5×10⁻⁴ degree Kelvin meter² perWatt between the inner surface and outer surface.
 7. Theheat-dissipating package of claim 1, wherein the sleeve is formed of amaterial with an index of refraction smaller than the index ofrefraction of the at least one cladding.
 8. The heat-dissipation packageof claim 1, wherein the sleeve is formed from a fluoroacrylate polymerand has a thickness ranging from approximately 5 microns toapproximately 30 microns.
 9. The heat-dissipation package of claim 1,wherein the sleeve has an axial length that is approximately the same asan axial length of the heat-generating section of the optical fiber. 10.The heat-dissipation package of claim 1, wherein the cover and the baseare each formed from silicon or tungsten.
 11. The heat-dissipationpackage of claim 1, wherein the cover is formed from a material that istransmissive to ultraviolet wavelength radiation.
 12. Theheat-dissipation package of claim 1, wherein the cover is formed frommultispectral zinc sulphide or synthetic sapphire.
 13. Theheat-dissipation package of claim 1, wherein the base is formed from amaterial that has a thermal conductivity greater than 50 Watts per meterdegree Kelvin and a coefficient of thermal expansion less than 5×10⁻⁶per degree Kelvin.
 14. The heat-dissipation package of claim 1, whereinthe cover is formed from a material that has a thermal conductivitygreater than 20 Watts per meter degree Kelvin and a coefficient ofthermal expansion less than 7×10⁻⁶ per degree Kelvin.
 15. Theheat-dissipation package of claim 1, further comprising a housingincluding a body and a lid, the body including a central cavityretaining the base and the cover and opposing ends, each end having achannel configured to receive a portion of the optical fiber.
 16. Theheat-dissipation package of claim 15, wherein the body is formed from amaterial that has a thermal conductivity greater than 50 Watts per meterdegree Kelvin and a coefficient of thermal expansion less than 5×10⁻⁶per degree Kelvin.
 17. The heat-dissipation package of claim 15, whereinthe body is formed from tungsten.